In steam generators, heating surface is normally disposed in the vertical rear pass leading from the furnace. The last heat exchange surface located within the rear pass is an economizer, where water flowing through the steam generating tubes is heated. Although the combustion gases passing over the economizer surface is relatively cool (not over 1500 F.), care must still be taken to support the horizontal runs of the internested sinuous or serpentine economizer tubes in a manner which will permit unequal thermal expansion to take place in the various horizontal tube runs, without placing undue stress in the tubes.